Physiological Disorders of Tomatoes

While tomatoes are easy to grow, insects and diseases can damage plants and reduce crop yields. Environmental stresses can cause additional problems. Physiological disorders of tomatoes include blossom end rot, fruit cracking, and sunscald.

Blossom end rot is a common problem on tomatoes. It appears as a brownish black spot on the blossom end (bottom) of the fruit. Secondary organisms invade the brownish black spot and cause the fruit to rot. Blossom end rot is most common on the earliest maturing fruit that ripen in July and early August.

Blossom end rot is caused by a calcium deficiency in the developing fruit. Wide fluctuations in soil moisture levels impair calcium uptake by the root system of the tomato plant. Excessive nitrogen fertilization may also contribute to blossom end rot.

To reduce blossom end rot, water tomato plants on a weekly basis during dry weather to provide a consistent supply of moisture to the plants. (Tomato plants require about 1 to 1 ½ inches of water per week during the growing season.) Mulch the area around the tomato plants to conserve soil moisture. Avoid over-fertilization. There is no need to apply calcium to the soil as most Iowa soils contain more than adequate levels of calcium.

Pick and discard fruit affected with blossom end rot. The removal of the affected fruit will allow the tomato plant to channel all of its resources into the growth and development of the remaining fruit.

Fruit cracking is another common problem. Cracks usually appear at the top or stem end of the fruit. Cracks radiate out from the stem (radial cracks) or circle the fruit in concentric rings (concentric cracks). Like blossom end rot, fruit cracking is associated with wide fluctuations in soil moisture levels. A heavy rain or deep watering after a long, dry period results in rapid water uptake by the plant. The sudden uptake of water results in cracking of ripening fruit. Generally, fruit cracking is most common on the large, beefsteak-type tomatoes.

As with blossom end rot, fruit cracking can be reduced by supplying the tomato plants with a consistent supply of moisture during the summer months. During dry periods, a thorough soaking once every 7 days should be adequate for most tomato plants. Conserve soil moisture by mulching the area around tomato plants with dried grass clippings, straw, shredded leaves or other materials. Also, plant tomato varieties that possess good crack resistance. Tomato varieties that possess good to excellent crack resistance include Jetstar and Mountain Spring.

Sunscald initially appears as shiny white or yellow areas on the sides of the fruit exposed to the sun. Later, the affected tissue dries out and collapses, forming slightly sunken, wrinkled areas. Secondary organisms invade the affected areas causing the fruit to rot. Sunscald occurs on fruit exposed to the sun during periods of extreme heat.

Losses due to sunscald can be reduced by growing tomatoes in wire cages. Cage grown tomato plants provide good foliage protection for the fruit. Also, control Septoria leaf spot and other foliar diseases which defoliate the plants and expose the fruit to direct sunlight.

Despite the loss of a few tomatoes to blossom end rot, fruit cracking, or sunscald, most tomato plants will produce a good crop with proper care.


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